Picture receiving system



Dec. 31, 1940.. i K. SCHLESINGER 2,226,992

PI C'I'URE RECEIVING SYSTEM Filed Dec. 5, 1954 76 Bacall/5.6 7175! Patented Dec. 31, 1940 PATENT, OFFICE 2,226,992 7 PICTURE RECEIVING SYSTEM Kurt Schlesinger, Berlin, Germany, assignor, by

mesne assignments, to Loewe Radio, Inc., a corporation of New York Application December 5, 1934, Serial No. 756,125 In Germany December 6, 1933 3 Claims.

The subject matter of the present invention is an arrangement forthe synchronising of electrical apparatus, especially television arrangements using relaxation oscillation generators.

According to the invention, there are employed for synchronising purposes negative impulses of constant value. Owing to the use of impulses of constant value the-selection thereof in the receiver is considerably facilitated.

In the application Serial No. 725,743 there is described an arrangement for the reception of television picture contents voltages and synchronising impulses both modulating the same carrier wave, the synchronizing impulses being of constant negative value. In this arrangement the impulses are separated from the contents'of the image by a high-vacuum tube, with or without grid, so that merely the highest potential values, 1. e. the synchronizing impulses are capable of being effective on the relaxation oscillation generators for synchronising purposes. In this way the synchronisation impulses are separated from the image current.

The subject matter of the invention is an ad- 25 ditional development of this arrangement.

According to the invention, there is employed in place of the high-vacuum amplifier tube for separation of the synchronisation impulses a hot-cathode tube having a filling of gas, the gas pressure preferably being selected such that the discharge current traversing the valve immediately develops its full strength after the ignition potential is reached (approximately 10- 10" mm. noble gas).

The invention is best understood by referring to the drawing, wherein:

Figure 1 shows one form of the present invention, and

Figure 2 shows a modified form of the present 40 invention.

In Fig. 1, I is the audion stage. As such there may be employed the ultra-audion with freely oscillating grid coil 2 and twin-grid tube 3 set forth by the applicant in the application Ser. No. 747,011.

It is assumed that synchronisation impulses are employed which exceed the image impulses in a negative direction, for example by twice the extent.

5 At the anode resistance 4 (for example approximately 5000 ohms) thereare accordingly produced during a synchronisation impulse powerful negative potentials against earth, which are transmitted over the large condenser 5 (1 m. f. to the l e ancl' fro there further to the image-receiving tube. The condenser 5 is conveniently selected in such fashion that the same also allows passage of a frequency of 25 cycles. The condenser 1 on the other hand is intended merely for transmission of the syn- 5 chronisation impulses to the glow lamp 9, having the hot cathode 2|, employed according to the invention. The long synchronisation impulses. may be selected, for example, at approx-' imately 1 millisecond, this order of impulse cor- 1o responding with, say 3-5 lines of a 200-line image; "I may accordingly be selected at 2 10 m. f. and the resistance 8 at 70,000 ohms.

The particular advantage when using the gasfilling according to the invention consists in the fact that the discharge current traversing the tube 9 develops its full force immediately upon the ignition potential being surpassed, which potential is extremely precisely defined and amounts to approximately volts, whereas in the case 20 of high-vacuum tubes the anode current has a preparatory range of a curved nature which is subject to space charge. The resistance of the glow lamp 9 may accordingly be ignored after the commencement of the ignition, so that the resistance of the total current path is represented in substance merely by the inner resistance of 3 in parallel with the small anode resistance 4 and the condenser l. comparatively strong currents are accordingly obtained immediately the ignition value has been exceeded.

The response potential of 9 is regulated by a variable bias I 0. According to the invention, the response potential is so, adjusted that the same does not appreciably exceed the highest nega- 5 tive image potential occurring in practice. The same is dependent, therefore, on the sensitiveness of the television ,tubeemployed, and when using the modern television tubes at present employedin practice may be adjusted at approximately 15 volts. The amount of negative bias suppplied by the battery l0 should be selected accordingly in such fashion that by reason of the bias the difference is compensated between.

the ionisation potential (ignition. potential) of the tube 9 and the desired response potential. Owing to the use of glow lamps it is possible,

in addition to utilisation of theimpulse current components for synchronisation purposes, which takes place by means of the transformers H for the short-line impulse and I2 for the long imageechange impulse, to charge a suitably selected condenser not only to the D. C. mean value but also to the peak value of the synchronisation impulse, from which merely the potential value of the commencing ignition is deducted. With the stated values, i. e., with an impulse potential of approximately 25 volts and a response voltage of the device amounting to approximately 15 volts, it is possible, for example, to charge the condenser I3 to -10 volts against earth. The potential at l3 increases in proportion to the stated excess potential. This effect may only be accomplished if the highly ohmic leak l4 connected in parallel with [3 is so selected in accordance with the invention that its conductivity may be ignored as compared with that of the circuit being charged, which is particularly the case in connection with gas-filled amplitude filters 9 according to the invention. The potential forming at the condenser I3 is conducted as grid bias over a line l9 to the receiving amplifier tubes. For the sake of amplification regulation lacking as far as possible any inertia, the capacity Iii/according to the invention, is made so small that the same is charged as far as possible in a fraction of a lineiperiod. The same on the other hand should be at least so large that its A. C. resistance always remains small as compared with the A. C.-resistances present in the charging circuit, so that the charging current itself is not weakenled. In practice l3 for example may be selected at approximately 10- .m. f. and the resistance [4 atapproximately .510 ohms. According to the invention, the circuit 'l3/l4 is preferably so adjusted that the same possesses a time constant of 'at least one line period or more.

According, to the invention, the direct potential thus obtained which is an automatic volume or gain potential is conducted over the line It simultaneously to as many amplifier tube grids as may be possible in the receiver dependent'on the connection system. In this manner the bias necessary to compensate fading may be considerably reduced.

If the receiver contains merely few amplifier tubes, it is possible under certain circumstances according to the invention to provide a special D. C. amplifier tube for increasing the regulating potential.

In this case, as illustrated by way of example in Fig. 2, it is possible to provide a D. C. resistance M in the cathode lead of the tube, so that the bias is positive against earth. The anode circuit is completed in direct fashion against earth over the stated transformers II and I2. There may then be connected in direct fashion with the cathode of the glow tube 9 a D. C. amplifier tube l5 in the manner indicated diagrammatically in the drawing, whereby, with the assistance of a filter chain l1, l8, both the short as Well as the long impulse signals and all image current frequencies of the line 6 require to be withheld from the grid of this tube.

A filter chain of this nature may consist, for example, of a resistance l! of approximately I0 ohms and a condenser l8 of approximately Ill mf. The same, however, may also be constructed as a multiple member chain, and in accordance with the invention should preferably always be so dimensioned that its resulting oscillation initiation period does not considerably surpass a-few line periods. a

As regards the devising of the transformers l I and i2, these have the object of converting the line impulses, which are negative in themselves, into positive control impulses, by means of which the discharges in the scanning oscillation generators thru the tubes 22 (indicated in Fig. 1 for the line circuit) are actuated.

The invention is naturally not restricted to the forms of embodiment quoted merely by way of example, and may be modified without difficulty in its details without departing from the fundamental idea of the invention.

I claim:

1. A television receiving system including means to demodulate a carrier signal to produce a composite series of picture and synchronizing signalswith the synchronizing signals extending in a negative direction and having an intensity greater than any picture signals, a discharge tube havinga cathode'and an anode, a load circuit, means for connecting one end of the load circuit to the anode of said tube, a time constant circuit including a parallel connected condenser and resistance, means for connecting one end of the time constant circuit to a point of fixed potential, means for connecting the other end of the time constant circuit. to the other end of the load circuit, means for impressing the produced series of composite signals uponthe cathode of said tube, and means for biasing the cathode with respect to the point of fixed potential by an amount sufficient to normally bias the tube to cut-off exceptwhen synchronizing signals are applied to the cathode thereof, whereby the synchronizing signals of the composite series will be separate from the picture signals and will appear acrossthe load circuit, and whereby desirable automatic volume control voltages will be produced at the junction of the time constant circuit and the load circuit to compensate for fading and variations in the strength of the received carrier signal where the variations in the received signal strength is at least of the order of five to one.

2. A television receiving system including means to demodulate a carrier signal to produce a composite series of picture and synchronizing signals with the synchronizing signals extending in a negative direction. and having an intensity greater than any picture signal including black, a gaseous discharge tube having a cathode and an output electrode, a load circuit including means responsive to synchronizing signals, means for connecting one end of the load circuit to the output electrode of said tube, a time constant circuit including a condenser and a resistance connected in parallel, means for connecting one end of the time constant circuit to a point of ages will be produced at the junction of the time constant circuit and the load'circuit to compensate for fading and variations in the strength of the received carrier signals when such variations exceed a ratio of at least five to one.

3. A television receiving system including means to demodulate a carrier signal to produce a composite series of picture and synchronizing signals with the synchronizing signals extending in a-negative direction and having an intensity greater than any picture signals, a discharge tube having a cathode and an anode, a load circuit including means responsive to synchronizing signals, means for connecting one end of the load circuit to the anode of said tube, a time constant circuit including a parallel combination of a condenser and a resistance, means for connecting one end of the time constant circuit to ground potential, means fior connecting the other end of the time constant circuit to the other end of the load circuit, means including a condenser for impressing the produced series of composite signals upon the cathode of said tube, means including a source of potential and the time constant circuit for normally biasing the cathode with respect to ground potential and accordingly with respect to said anode, by an amount surficient to normally prevent appreciable conduction of the tube except when signals of the intensity of synchronizing signals are applied to the cathode thereof, whereby the synchronizing signals will be separated from the picture signals and will appear across the load circuit, and whereby a desirable automatic gain control voltage will be produced at the junction of the time constant circuit and the load circuit to compensate for fading and variations in the strength of the received carrier signal for all variations in the strength of the received carrier in excess of the order of five to one.

KURT SCI-ILESINGER. 

